Imaging element and imaging apparatus

ABSTRACT

An imaging element includes a red color filter, a blue color filter, and two kinds of first and second green color filters. The first green color filter has a peak spectral sensitivity in a longer wavelength region than a wavelength of a peak spectral sensitivity of the second green color filter.

BACKGROUND

1. Technical Field

The present disclosure relates to an imaging element having a pluralityof kinds of color filters, and an imaging apparatus provided with theimaging element.

2. Related Art

JP2000-196952A discloses an imaging apparatus. This imaging apparatuscan control a shot image according to adaptation to luminosity. That is,the imaging apparatus controls the shot image to increase a blue colorsensitivity increases as the image becomes dark, and increase a redcolor sensitivity as the image becomes bright.

Thus, the imaging apparatus can shoot an image applied with adaptationto luminosity similar to that of a human eye.

SUMMARY

The imaging apparatus disclosed in JP2000-196952A may be able tosufficiently control a blue component and a red component according to abrightness level of the captured image. However, the imaging apparatusdisclosed in JP2000-196952A cannot sufficiently control a greencomponent according to the brightness level of the shot image.

It is an object of the present disclosure to provide an imaging elementand an imaging apparatus capable of sufficiently controlling a greencomponent according to a brightness level of a captured image.

An imaging element of present disclosure is an imaging element forgenerating an image signal based on the incident light, comprising a redcolor filter; a blue color filter; and two kinds of first and secondgreen color filters.

The first green color filter has a spectral sensitivity peak in awavelength region higher than the wavelength of a spectral sensitivitypeak of the second green color filter.

An imaging apparatus of present disclosure includes the imaging elementin the above and a controller that corrects image signals generated bythe imaging element according to the illumination level of a subject andgenerating brightness signals.

The imaging element and the imaging apparatus in the above aspects cansufficiently control the green component according to the brightnesslevel of the captured image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a configuration of a digital video cameraaccording to a first embodiment;

FIG. 2 is a plan view showing an arrangement of color filters accordingto the first embodiment;

FIG. 3 is a view showing spectral sensitivity of each of color filtersof a CMOS image sensor according to the first embodiment;

FIG. 4 is a flowchart for describing an operation for generating abrightness signal from a captured image according to the firstembodiment;

FIG. 5 is a view showing a relationship to calculate a coefficient forobtaining a correction signal for a green color according to the firstembodiment;

FIG. 6 is a plan view showing an arrangement of color filters (1)according to another embodiment;

FIG. 7 is a plan view showing an arrangement of color filters (2)according to another embodiment;

FIG. 8 is a plan view showing an arrangement of color filters (3)according to another embodiment;

FIG. 9 is a plan view showing an arrangement of color filters (4)according to another embodiment;

FIG. 10 is a plan view showing an arrangement of color filters (5)according to another embodiment; and

FIG. 11 is a view showing spectral sensitivity of color filtersaccording to a comparison example.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the accompanying drawings appropriately, the embodimentswill be described in detail below. However, some detailed descriptionthereof will be omitted more than necessary. For example, a detaileddescription of well-known matters and a duplicate description for theconfiguration of substantially the same matter may be omitted. This isto avoid causing description to be unnecessarily verbose, and tofacilitate the understanding of those skilled in the art. It should benoted that the inventor provide accompanying drawings and the followingdescription in order to cause those skilled in the art to fullyunderstood the present disclosure. It is not intended to limit thesubject matter of the claims by those.

Hereinafter, an embodiment will be described with a digital video camera(imaging apparatus) provided with a CMOS image sensor (imaging element)as one example, with reference to the drawings.

1. First Embodiment

1-1. Configuration of Digital Video Camera (Imaging Apparatus)

First, an example of an electrical configuration of a digital videocamera according to a first embodiment will be described with referenceto FIG. 1. FIG. 1 is a block diagram showing a configuration of adigital video camera 100. The digital video camera 100 is an imagingapparatus which captures an image of a subject image formed by anoptical system 110 including one or more lenses with a CMOS image sensor140.

Image data generated by the CMOS image sensor 140 is subjected tovarious processes by an image processor 160, and is stored in a memorycard 200. The configuration of the digital video camera 100 will bedescribed in detail below.

The optical system 110 includes a zoom lens and a focus lens. By movingthe zoom lens along an optical axis, the subject image can be enlargedor reduced. In addition, by moving the focus lens along the opticalaxis, a focus of the subject image can be adjusted.

A lens driver 120 drives various kinds of lenses included in the opticalsystem 110. The lens driver 120 includes a zoom motor for driving thezoom lens, and a focus motor for driving the focus lens.

A diaphragm unit 300 adjusts a size of an aperture for light, accordingto settings by a user or automatically, to adjust an amount of light tobe transmitted.

A shutter unit 130 is a unit for blocking the light to be transmitted tothe CMOS image sensor 140.

The CMOS image sensor 140 captures the subject image formed by theoptical system 110, to generate image data. The CMOS image sensor 140includes a color filter 141 (it will be described in detail later), aphoto detector, and an AGC (gain control amplifier). The photo detectorconverts an optical signal collected by the interchangeable lens 101 toan electrical signal to generate image information. The AGC (gaincontrol amplifier) amplifies the electrical signal that is output fromthe photo detector. The CMOS image sensor 140 further includes a drivingcircuit to perform various kinds of operations such as exposure,transfer, and electrical shutter. A detail thereof will be describedlater.

An A/D converter 150 converts analog image data generated by the CMOSimage sensor 140 to digital image data.

The image processor 160 performs various processes for the digital imagedata which is generated and converted by the CMOS image sensor 140,under control of a controller 180. The image processor 160 generatesimage data to be displayed on a display monitor 220, and generates imagedata to be stored in the memory card 200. For example, the imageprocessor 160 performs various processes such as a gamma correction,white balance correction, and defect correction for the image datagenerated by the CMOS image sensor 140. In addition, the image processor160 compresses the image data generated by the CMOS image sensor 140according to a compression format compliant with H.264 standard, MPEG 2standard, or the like. The image processor 160 can be implemented by aDSP or a microcomputer.

The controller 180 is a controlling unit for controlling a whole digitalvideo camera 100. The controller 180 can be implemented by asemiconductor element. The controller 180 may be configured only byhardware, or may be implemented by combination of hardware and software.The controller 180 can be implemented by a microcomputer.

A buffer 170 functions as a work memory of the image processor 160 andthe controller 180. The buffer 170 can be implemented with a DRAM or aferroelectric memory.

A card slot 190 is a slot which a memory card 200 can be inserted intoand removed from. The memory card 200 can be mechanically andelectrically connected to the card slot 190.

The memory card 200 includes therein a flash memory or the ferroelectricmemory, and can store data such as an image file generated by the imageprocessor 160.

An internal memory 240 is configured by the flash memory or theferroelectric memory. The internal memory 240 stores a control programor the like used for controlling the whole digital video camera 100.

An operation unit 210 is a general term for a user interface whichreceives an operation from a user. The operation unit 210 includes, forexample, arrow keys and a decision button through which the operationfrom the user can be received.

A display monitor 220 can display an image (through image) representedby an image data generated by the CMOS image sensor 140, and an image ofimage data read from the memory card 200. In addition, the displaymonitor 220 can display various kinds of menu screens used forconfiguring various kinds of settings on the digital video camera 100.

1-2. Configuration of CMOS Image Sensor

Next, a configuration of the CMOS image sensor according to the firstembodiment will be described with reference to FIGS. 2, 3, and 11. FIG.2 is a plan view showing a color filter 141 provided in the CMOS imagesensor 140. FIG. 3 is a schematic view for describing spectralsensitivity of each of color filters used in the CMOS image sensor 140.FIG. 11 is a schematic view for describing spectral sensitivity of colorfilters of a comparison example, and explains a reason why the colorfilters having the spectral sensitivity shown in FIG. 3 are used.

As shown in FIG. 2, the CMOS image sensor in this example has four kindsof color filters arranged in a matrix shape along a row direction and acolumn direction. Specifically, the CMOS image sensor 140 has two kindsof green color filters (G1 and G2), one kind of red color filter (R),and one kind of blue color filter (B).

The two kinds of green color filters of different spectral sensitivity(G1 and G2) are arranged in a checkered pattern in the row direction andcolumn direction in the CMOS image sensor 140. In addition, the twokinds of green color filters of different spectral sensitivity (G1 andG2) are arranged complementarily with respect to each other in the rowdirection and the column direction in the CMOS image sensor 140.

The red and blue color filters (R and B) are arranged complementarilywith respect to the green color filter (G1) in the row direction andcolumn direction in the CMOS image sensor 140. In addition, anarrangement order of the red and blue color filters (R and B) in the rowdirection is reversed with respect to each column in which they arearranged.

Although not illustrated herein, light which passed through each colorfilter is converted to predetermined image data by the driving circuitincluding a photodiode. In addition, a microlens or the like used forcollecting the light is arranged on each color filter.

Spectral Sensitivity of Color Filter (First Embodiment)

Here, the spectral sensitivity of each color filter is as shown in FIG.3. More specifically, the blue color filter (B) has a peak (maximumvalue) of the spectral sensitivity in a neighborhood of a shortwavelength of 400 nm. The red color filter (R) has a peak (maximumvalue) of the spectral sensitivity in a neighborhood of a longwavelength of 600 nm. The one color filter (G1) of the two kinds ofgreen color filters with different spectral sensitivity has a peak(maximum value) P1 of the spectral sensitivity in a neighborhood of 550nm. The other color filter (G2) of the two kinds of green color filtersof different spectral sensitivity has a peak (maximum value) P2 of thespectral sensitivity in a neighborhood of 500 nm. Although in thisembodiment, the peak of the spectral sensitivity of the one color filter(G1) is set to 550 nm, it may be set to a value shifted from 550 nm inthe range of ±20 nm. In addition, although the peak spectral sensitivityof the other color filter (G2) is set to 500 nm, it may be set to avalue shifted from 500 nm in the range of ±20 nm.

Here, the wavelengths 500 nm and 550 nm corresponding to the peaks P1and P2 of the spectral sensitivity of the two kinds of green colorfilters with different spectral sensitivity (G1 and G2), respectivelyare wavelengths selected according to the characteristic of spectralluminous efficiency of a human eye. That is, the human eye recognizes anobject by working a rod cell which mainly recognizes light in theneighborhood of 500 nm in a dark place (spectral luminous efficiency indark place). In addition, the human eye recognizes an object by workinga cone cell which mainly recognizes light in the neighborhood of 550 nmin a bright place (spectral luminous efficiency in bright place).

Thus, according to the first embodiment, as described above, at leastthe two kinds of green color filters with different spectral sensitivity(G1 and G2) corresponding to the characteristic of spectral luminousefficiency of a human eye are arranged in the CMOS image sensor 140.Then, by adjusting a weighting degree of the light received through eachcolor filter, according to the brightness of the object (that is, thebrightness of the periphery of the digital video camera), the imagelikely to be recognized by the human eye can be captured.

As described above, the green color filters (G1) are arranged in thecheckered pattern in the CMOS image sensor 140, so that a resolution ofa brightness signal of the captured image can be prevented fromreducing.

The green color filter (G2) is arranged complementarily with respect theother green color filter (G1) in the CMOS image sensor 140. Thus, evenwhen illuminance of the object is low, the sensitivity can be kept at acertain level or more.

In addition, the red color filter (R) and the blue color filter (B) arearranged in reverse with respect to each column. In other words, thearrangement of the red and blue color filters (R and B) in the rowdirection is reversed with respect to each column in which they arearranged. With this arrangement, moire is prevented from being generatedin the captured image.

As described above, according to the first embodiment, one kind of greencolor filter (G) having spectral sensitivity including the wavelength of500 nm and the wavelength of 550 nm is not used. The two kinds of greencolor filters (G1 and G2) having the peak of the spectral sensitivity onthe wavelength of 500 nm and the wavelength of 550 nm, respectively areintentionally used.

Spectral Sensitivity of Color Filter (Comparison Example)

Meanwhile, according to the comparison example, one kind of green colorfilter (G) having spectral sensitivity including the wavelength of 550nm is used. The spectral sensitivity of each color filter in thiscomparison example is as shown in FIG. 11. As shown in FIG. 11, in thecomparison example, one kind of green color filter (G) having a peak inthe vicinity of 550 nm must be used to configure the illuminance.Therefore, it is possible to follow the characteristic of spectralluminous efficiency of a human eye in the bright place, but it isimpossible to follow the characteristic of spectral luminous efficiencyof a human eye in the dark place. In addition, even if the peak of thespectral sensitivity is set in the vicinity of 500 nm, it is possible tofollow the characteristic of spectral luminous efficiency of a human eyein the bright place, on the other hand, it is impossible to follow inthe dark place.

1-3. Operation for Generating Brightness Signal (Y) from Captured Image

Next, a description will be given on an operation for generating abrightness signal (Y) from the image captured by the CMOS image sensor140 in the digital video camera 100 according to the first embodiment,with reference to FIGS. 4 and 5. FIG. 4 is a flowchart showing anoperation performed when the brightness signal (Y) is generated from thecaptured image. FIG. 5 is a schematic view showing a relationship ofcoefficients K1 and K2 to generate the brightness signal.

Here, especially, a description will be given, by way of example, on anoperation processed when the brightness signal (Y) is generated under acondition that the illuminance of the object (the brightness of theimage) is lower than a certain level and the diaphragm unit 300 is in anopen state (state in the dark place). The description will be given withthe flowchart in FIG. 4.

(Step S100)

First, when the digital video camera 100 is set to a shooting mode bythe user, an operation for capturing an image of RAW data (data beforedevelopment) is started by the CMOS image sensor 140.

(Step 110)

After the start of capturing the RAW data, the controller 180 determinesan AGC (Automatic Gain Control) gain, based on brightness information ofthe captured RAW data. It is noted that AGC gain is determined dependingon the illuminance of the subject in the image, the value of the AGCgain becomes higher as the illuminance of the subject becomes lower.

(Step S120)

After determining the AGC gain, the controller 180 calculates thecoefficients K1 and K2 based on the determined AGC gain. Here, thecoefficients K1 and K2 are coefficients by which the RAW data G1 and G2of the green color filters are multiplied for weighting, as correction,as shown in the following equation (1) to calculate a green colorcorrection signal G′. More specifically, in this example, the controller180 calculates the coefficients K1 and K2, according to the relationshipwith the AGC gain shown in FIG. 5.

G′=K1×G1+K2×G2   (1)

As shown in FIG. 5, the coefficient K2 is set so that its valueincreases as the AGC gain increases (in the dark place where theilluminance of the object is low). Meanwhile, the coefficient K1 is setso that its value increases as the AGC gain decreases (in the brightplace where the illuminance of the object is high).

Therefore, according to this example, when the illuminance of the objectis low (state in the dark place), the value of the coefficient K2 isgreater than the value of the coefficient Kl. Therefore, when theilluminance of the object is high (state in the bright place), thecorrection is made such that the weighting of the RAW data G2 of thegreen color filter on a short wavelength side is relatively greater thanthe weighting of the RAW data G1 of the green color filter on a longwavelength side. Thus, as will be described later, the digital videocamera 100 can generate an image which reproduces green color likely tobe recognized in the dark place by the human eye.

In addition, as shown in FIG. 5, according to the first embodiment, thevalues of the coefficients K1 and K2 are set to linearly changeaccording to the value of the AGC gain. Thus, the kind of green colordoes not rapidly change, and therefore the image which does not leave afeeling of strangeness in the human eye can be generated at the time ofswitching between the dark place and the bright place.

In this example, the coefficients K1 and K2 are both not less than 0 andnot more than 1 (0≦K1≦1, and 0 K2≦1). In addition, a sum of thecoefficients K1 and K2 is equal to 1 (K1+K2=1). These are set in orderto ensure color reproducibility and prevent the green color component Gfrom increasing or decreasing.

(Step S130)

Then, the controller 180 calculates a value of the green color compositesignal G′ with the calculated coefficients K1 and K2. More specifically,as shown in equation (1), the controller 180 calculates the green colorcomposite signal G′ according to the illuminance of the subject, byassigning the values of the coefficients K1 and K2 and the RAW data G1and G2 of the green color filter.

(Step S140)

Then, the controller 180 calculates a low frequency component (YL) of abrightness signal (Y), according to the following equation (2).

YL=0.3×RL+0.59×G′L+0.11×BL   (2)

As shown in equation (2), the low-frequency component (YL) of thebrightness signal (Y) is calculated by assigning the value of thelow-frequency component RL of the pixel output R of red color filters,the value of the low-frequency component BL of the pixel output B ofblue color filters, the value of the low-frequency component G′L of thegreen color composite signal G′ calculated in the step S130. Inaddition, the low-frequency component G′L of the green color compositesignal G′ in the equation (2) is calculated, by using the low-frequencycomponent G1L of the pixel output G1 from green color filters (G1)arranged in a checkerboard pattern, and the low-frequency component G2Lof the pixel output G2 from color filters (G2) arranged complementarily,and the following equation (3).

G′L=K1×G1L+K2×C2L   (3)

Meanwhile, the high-frequency component (YH) of the brightness signal(Y) , as shown below, is configured using the high-frequency componentG1H of the pixel output 31 from green color filters (G1) arranged in acheckerboard pattern, and the high-frequency component G2H of the pixeloutput 32 from color filters (G2) arranged complementarily.

YH=G1H+G2H   (4)

(Step S150)

Then, the controller 180 generates a wideband brightness signal (Y) byadding the high-frequency component YH and the low-frequency componentYL of the luminance signal as shown in the following equation (5).

Y=YL+YR   (5)

Here, in the dark place in this example, the weighting (K2) of the RAWdata G2 of the green color filter having a peak of sensitivity on shortwavelength side, is relatively large compared with the weighting (K1) ofthe RAW data G1 of the green color filter having a peak of sensitivityin long wavelength side, and the green color composite signal G′ isgenerated according to the illuminance of the subject (S130). Therefore,the brightness signal YL is calculated according to the low-frequencysignal G′L of the correction signal G′ generated by the weighted RAWdata G1 and G2 as described above (step 140). As a result, the widebandbrightness signal (Y) is generated corresponding to correction signal G′to be suitable for the dark place.

On the other hand, in the state where the illuminance of the object ishigher than a certain level and the diaphragm unit 300 is near to close(state of the bright place), the relationship between the coefficientsK1 and K2 is opposite to the state of the dark place. That is, as shownin FIG. 5, in the bright state, the weighting coefficient K1 of the RAWdata G1 of the green color filter having a peak of sensitivity in longwavelength side is set to be relatively large compared with theweighting coefficient K2 of the RAW data G2 of the green color filterhaving a peak of sensitivity in short wavelength side.

2-4. Function and Effect

According to the first embodiment, at least the following effects areprovided.

That is, by changing the configuration which is mainly composed of G′which is the main component in the brightness signal according to thelevel of illuminance of the subject, the brightness signal can bereproduced easily which is suitable for characteristic of spectralluminous efficiency of a human eye.

The controller 180 provided in the imaging apparatus 100 corrects theimage signal generated through the two kinds of first and second greencolor filters (G1 and G2) with different spectral sensitivity with thepredetermined coefficients (K1 and K2), according to the illuminancelevel of the object, and controls the generation of the brightnesssignal (Y).

More specifically, the controller 180 in this example calculates thecoefficients K1 and K2 according to the relationship with the AGC gain(illuminance) shown in FIG. 5. As shown in FIG. 5, the coefficient K2 isset so that its value increases as the AGC gain increases (as theilluminance of the subject decreases in the dark place). Meanwhile, thecoefficient K1 is set so that its value increases as the AGC gaindecreases (as the illuminance of the subject increases in the brightplace) (step S120).

Therefore, according to equation (1), for an image with low illuminance(state in the dark place), the green color correction signal G′ iscalculated so that the weighting coefficient K2 of the RAW data G2 thegreen color filter on the short wavelength side is relatively greaterthan the weighting coefficient K1 of the RAW data G1 of the green colorfilter on the long wavelength side (step S130).

The calculated green color correction signal G′ is used for calculatingthe low frequency component (YL) of the brightness signal, according toequation (2). That is, a contribution ratio on the lower frequency sideis improved in calculating the low frequency component (YL) of thebrightness signal (step S140).

Thus, the brightness signal (Y) is generated by adding the low frequencycomponent (YL) of the brightness signal and the high frequency component(YH) of the brightness signal (step S150).

As described above, in the present embodiment, as shown in FIG. 5, inthe state the illuminance of the subject is low (in the state the AGCgain is high), the coefficient K2 for RAW data G2 from the green filterhaving a peak of sensitivity on short wavelength side is set larger. Inother words, in generating the composite green signal G′, as theilluminance of the subject is low, the weighting of the image data G2from the green color filter having a peak of sensitivity on shortwavelength side is set greater. Thus, an image can be generated, whichreproduces the green easily visible to the human eye in the dark place.This is based on the visual feature that recognizes the object byworking the rod cell which mainly recognizes the light (G2) having thewavelength of the neighborhood of 500 nm on the short wavelength side,in the dark place.

In addition, the values of the coefficients K1 and K2 are set tolinearly change according to the value of the AGC gain. Thus, the kindof green color does not rapidly change, so that the image which does notprovide the feeling of strangeness in the human eye can be generated atthe time of switching between the dark place and the bright place.

In this example, the coefficients K1 and K2 are both not less than 0 andnot more than 1 (0≦K1≦1, and 0≦K2≦1). In addition, the sum of thecoefficients K1 and K2 is equal to 1 (K1+K2=1). These are set in orderto ensure the color reproducibility and prevent the green colorcomponent G from increasing or decreasing.

2. Other Embodiments

The first embodiment has been described as one example of theembodiment. However, the embodiment is not limited to the above. Otherembodiments will be described below.

According to the first embodiment, the CMOS image sensor 140 has beendescribed as one example of the imaging unit, but the imaging unit isnot limited thereto. For example, a CCD image sensor or an NMOS imagesensor may be used as the imaging unit.

In addition, the image processor 160 and the controller 180 may beconfigured by one semiconductor chip, or separate semiconductor chips.

In addition, according to the first embodiment, as shown in FIG. 5, thecoefficients K1 and K2 are set to linearly change according to the AGCgain. However, the present embodiment is not limited to thisconfiguration. As another configuration, for example, the correctionsignal G′ may be generated by selectively using either one of the greencolor RAW data G1 or G2 according to the predetermined AGC gain. Thus,the image likely to be recognized by the human eye even in the darkplace can be generated with a simple configuration.

In addition, according to the first embodiment, the spectral sensitivityof the green color filters (G1 and G2) has the same shape. However, thepresent embodiment is not always limited to this example. For example,the spectral sensitivity of the green color filter G2 spreads toward thebottom more widely than the spectral sensitivity of the green colorfilter G1. Thus, an image having higher sensitivity in the dark placecan be generated.

In addition, according to the first embodiment, the brightness signal(Y) is calculated from the sum of the low frequency component (YL) ofthe brightness signal and the high frequency component (YH) of thebrightness signal. However, the present embodiment is not always limitedto this example. For example, a ratio of the high frequency component(YH) of the brightness signal in the following equation (6) may bereduced as the AGC gain increases (that is, as the illuminance of theobject reduces). Thus, an S/N ratio of the captured image can beimproved.

Y=YL+α×YH   (6)

In addition, according to the first embodiment, the coefficients K1 andK2 are determined based on the AGC gain. However, the present embodimentis not always limited to this example. For example, the coefficients K1and K2 may be determined based on a color temperature of the capturedimage.

Furthermore, according to the first embodiment, the low frequencycomponent (YL) of the brightness signal is calculated with equation (2).However, the present embodiment is not always limited to thisconfiguration. For example, the following equation (7) may be used forthe calculation.

YL=0.25×RL+0.5×G′L+0.25×BL   (7)

In addition, according to the first embodiment, the color filters arearranged as shown in FIG. 3. However, it is not always necessary to takethis configuration. For example, the color filters (1) to (5) may bearranged as shown in FIGS. 6 to 10. That is, any arrangement can beemployed as long as the imaging element 140 has the two kinds of firstand second green color filters (G1 and G2).

As described above, the embodiments are described as examples of the artin the present disclosure. The detailed description and accompanyingdrawings are provided for the purpose. Accordingly, the configurationsthat are described in the detailed description and accompanying drawingsmay include not only the essential configurations but also those forillustrating the art described above, which are not essential to solvethe problem. Consequently, these configurations which are not essentialshould not be construed as essential matters immediately, even thoughthey are described in the detailed description and accompanyingdrawings. In the embodiments described above, various modifications,replacements, additions, and omissions will be made within the scope ofthe appended claims or their ecuivalents, because the embodiments areintended to illustrate the art in the present disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure can be applied to an imaging element and animaging apparatus having an imaging element that generates image databased on an incident light passing through a color filter.

1. An imaging element for generating an image signal based on anincident light comprising: a red color filter; a blue color filter; afirst green color filter; and a second green color filter, wherein thefirst green color filter has a peak spectral sensitivity in a longerwavelength region than a wavelength of a peak spectral sensitivity ofthe second green color filter.
 2. The imaging element according to claim1, wherein a wavelength of a first peak of the spectral sensitivity ofthe first green color filter is determined based on the characteristicof spectral luminous efficiency of a human eye in a bright place, and awavelength of a second peak of the spectral sensitivity of the secondgreen color filter is determined based on the characteristic of spectralluminous efficiency of the human eye in a dark place.
 3. The imagingelement according to claim 2, wherein the first peak is provided in aneighborhood of 550 nm, and the second peak is provided in aneighborhood of 500 nm.
 4. The imaging element according to claim 1,wherein the first and second green color filters are arranged in acheckered pattern and complementarily with respect to each other in arow direction and a column direction, the red and blue color filters arearranged complementarily with respect to the first green color filter inthe row direction and the column direction, and an order of arrangementof the red and blue color filters in the row direction is reversed foreach column.
 5. An imaging apparatus comprising: the imaging elementaccording to claim 1; and a controller that corrects an image signalgenerated by the imaging element according to illuminance level of asubject to generate a brightness signal.
 6. The imaging apparatusaccording to claim 5, wherein the controller corrects the brightnesssignal with a first coefficient applied to the first color filter, andhaving a value decreasing as the illuminance level of the subjectbecomes low, and a second coefficient applied to the second colorfilter, and having a value increasing as the illuminance level of thesubject becomes low.
 7. The imaging apparatus according to claim 6,wherein the first and second coefficients linearly change according tothe illuminance level of the subject.
 8. The imaging apparatus accordingto claim 6, wherein the first and second coefficients are both not lessthan 0 and not more than 1, and a sum of the first and secondcoefficients is equal to 1.